This invention relates to microbiological testing apparatus and methods, and more particularly to an improved system for facilitating the automatic incubation and reading of microbiological test trays.
A number of different types of microbiological testing are carried out in trays or strips (referred to herein collectively as "trays") which have a number of chambers known as test wells or cupules. Such trays are used, for example, to identify a microorganism, or to determine the susceptibility of that organism to a number of antimicrobics, which latter trays are called susceptibility trays. Typically, the test wells or cupules in the identification trays contain complex chemicals or reagents which in the presence of an active fermenting culture change color, become cloudy or otherwise indicate that fermentation is or has taken place. Similarly, in one known susceptibility test called the minimum inhibiting concentration (MIC) test, the wells contain different dilutions of various antimicrobics and a growth medium to determine the dilution level of the antimicrobic which is sufficient to kill and/or inhibit growth of the organism.
Conventionally, the test reagents and any growth medium or antimicrobics are placed into the test wells in the form of an aqueous solution and later lyophilized. A different combination of reagent or growth medium is charged into different wells so that a great number of individual reactions are performed in a physically small apparatus. For example, in the MIC tests, a regular pattern of wells arranged in rows and columns could be provided, each row of wells containing different antimicrobics. Within a row, the concentration of the antimicrobic would increase from well to well by a factor of, for example, 2. Of course, other dilution ratios could be used.
When a test is to be performed, a microorganism is innoculated into each of the test chambers with sufficient water to reconstitute the reagents. The test trays are then incubated at an appropriate temperature, such as 35-37 degrees Celsius for an extended period of time. After a predetermined period, the individual chambers are examined for the presence or absence of a reaction or indication of color change, or a change in turbidity. Heretofore, it is believed that the inspection of the wells for the presence or absence of a reaction or indication was done manually at least in part. Thus, individual trays each required the use of technician's time in the preparation, innoculation, incubation and reading of the results. Moreover, since different test trays might be needed to determine different characteristics of the microorganisms, the reading of a variety of different trays could be a fairly complex procedure.
Systems have been provided for automating at least a portion of the reading process. In one existing system for use in semi-automatically recording the results of microbiological tests, a test tray having a plurality of test wells arranged in a certain pattern is placed beneath a transparent keyboard. A light source projects light through the tray and the keyboard so that the user can view the tray with its test wells through the keyboard. The keys of the keyboard correspond to the test wells, so that the user presses the keys overlying those wells in which the certain test results have occurred in order to record the results of the tests conducted in the test wells. Such a method of reading the test wells requires a highly skilled technician and a good deal of technician's time. In addition, the incubation times for identification and susceptibility trays may be quite different, with the result that the user will be recording the results for a particular patient or specimen at two different times, with the possibility that the identification and susceptibility results might not be properly assigned to the same patient. Moreover, the difference in times of incubation for identification and susceptibility trays means that the user or operator must return twice to the incubator for each patient.